Bump on Sebastopol goslings belly

So, little one is 5 days old.
I noticed that he has a bump on his belly, and I don't remember any of the others having this.
He eats, poops normal, is growing, and very social. Is this of anything to be concerned about?

I know this might sound like a silly question, but how do you pronounce Sebastopol? I'm a huge fan of the breed, but as I don't have ANY goose enthusiast real life friends, I've never heard anybody pronounce it.